Free piston engine with antiknock means

ABSTRACT

A free piston engine in which knocking of the engine is prevented by changing the return energy available to move the piston in its compression stroke and hence to vary the compression ratio. The apparatus includes a condition responsive means associated with possible knocking of the engine, which controls some controlling means for varying the return energy. Where the free piston engine employs a bounce chamber for controlling the return energy, the controlling means may be effective to change the pressure in this bounce chamber. Where the free piston engine has two power pistons acting alternately on a single assembly, the pressure ratio may be varied by controlling the amount of fuel admitted into one or more of the power cylinders. The apparatus also contemplates means for changing the return energy if a movable member driven by the piston moves too far with respect to an associated stationary member.

United States Patent 1191 Braun FREE PISTON ENGINE WITH ANTIKNQCK Primary ExaminerManuel A. Antonakas MEANS Assistant Examiner-Daniel J. OConnor Attorney, Agent, or Firm-Dorsey, Marquart, [76] Inventor: Anton Braun, 6421 Warren Ave., W

Edina Minn. 55435 Wmdhorst, est & l-lalladay [22] Filed: Feb. 16, 1973 [57] ABSTRACT [21] Appl' 332988 A free piston engine in which knocking of the engine is prevented by changing the return energy available [52] US. Cl...... 123/46 R, 123/46 SC, 123/198 DA to move the piston in its compression stroke and [51] Int. Cl. F02b 71/00, F02d 39/10 h nce to ary he compression ratio. The apparatus [58] Fi ld of S r h 123/46 R, 46 SC, 198 DA includes a condition responsive means associated with possible knocking of the engine, which controls some [56] References Cited controlling means for varying the return energy.

UNITED STATES PATENTS Where the free piston engine employs a bounce cham- 2,409,218 10/1946 Lewis 123/46 for g l i the 2,461,224 2/1949 Meitzler 123/46 means may e e to c ange ?pressure 2,671,435 M1954 Spier ct al'm 123/46 bounce chamber. Where the free plston englne has 2,81 1,958 11/1957 Roush 123/46 two POWer Plstons actlng alternately a slngle assem- 2,916,025 12/1959 Klotsch 123/46 y the Pressure ratio y be varied y controlling 3,016,689 1/1962 Bayer et a1 123/46 the amount of fuel admitted into one or more of the 3,020,706 2/1962 Horgen power cylinders. The apparatus also contemplates 3924591 3/1962 et means for changing the return energy if a movable 3,118,434 1/1964 Kosoff 123/46 member driven by the piston moves too far with spect to an associatedstationary member.

16 Claims, 6 Drawing Figures 79 r. SOURCE OF CONTROL FLUID 1 B7 89 r 90X 2 AMPLIFIER 4301.

91 1 8| 76 75 78 so as has 40 1 as. 72 50 42 g 74 I 1 l 1e 31 N VT l r' 56 a4 l 111 ,21 71 E ,15 5

I 1 53 62 l 6 25 '1 Q s1 Y I I8 22 67 29 32 41 66 52 55 FREE PISTON ENGINE WITH ANTIKNOCK MEANS BACKGROUND OF THE INVENTIONS Numerous devices have been employed for adjusting the operation of an engine to prevent knocking. By knocking, as used in this application, is meant any abnormal combustion condition, such as preignition, autoignition or rumble resulting in abnormal pressure rises in the cylinder. Such knocking can cause severe damage to an engine and it also reduces the efficiency of the engine. On the other hand, the engine usually operates at its maximum efficiency just before it begins to knock. Hence, it is desirable to operate the engine as close as possible to the point at which it would knock but provide some means for reducing the tendency of the engine to knock. One of these is to change the point in the cycle at which the ignition means is achieved. Changing the nature of the fuel mixture also can be employed. Another very satisfactory expedient is that of reducing the compression ratio.

Normally, when an attempt has been made to reduce the compression ratio to reduce knocking, this has been done in connection with a crank shaft type of engine. This requires some complicated way of mechanically adjusting elements of the engine. These may be satisfactory for purposes such as testing the quality of a fuel where a special test engine can be employed but they are very impractical in connection with an operating engine intended for broad commercial applications.

SUMMARY OF THE PRESENT INVENTION The present invention is concerned with a free piston engine in which knocking is prevented by sensing an incipient knocking condition and changing the total return energy available to move the piston in its compression stroke and thus changing its compression ratio to reduce the tendency to knock. By adjusting the return energy from time to time so that the compression ratio is always near the maximum value possible for a given set of conditions without producing sustained knocking, very efficient operation of the engine is obtained.

Where the free piston engine'has a bounce chamber, the adjustment of the return energy can be accomplished by varying the pressure in the bounce chamber. In the case of a spark ignition engine with a positive bounce chamber, the pressurein the chamber is decreased when a knocking tendency occurs. Where the bounce chamber is a negative bounce chamber, the pressure is increased to prevent knocking.

Free piston engines are often employed to operate compressors. Where this is done, some of the compressed air in the compressor may be used to control the apparatus for adjusting the return energy. For example, the means for sensing incipient knock may control a pilot valve of a pressure motor, the pressure of which is supplied by the compressor driven by the free piston. In the case of a tandem type of free piston engine in which there are alternately acting power pistons each operating in its own power cylinder and in which one piston and cylinder acts to provide the return energy for the compression stroke of the opposite power piston and cylinder, the return energy for a cylinder in which a knock condition is incipient can be adjusted by varying the fuel supplied to the opposite cylinder. If desired, the fuel to both cylinders can be adjusted simultaneously. Since, however, a knocking condition may occur in one cylinder and not in another, it is desirable to employ either a sensor responsive to the occurence of a knocking condition in either cylinder or two sensors, each associated with a different cylinder. The de' livery of fuel may be adjusted by adjusting the output of a fuel injection apparatus. This fuel injection apparatus may be either of a mechanical or electrical type.

It is also contemplated that the apparatus for adjusting the return energy to adjust the compression ratio can incorporate means for detecting excessive movement of a member driven by the engine. It is customary to employ some energy absorbing device in connection with such a free piston engine, this energy absorbing device constituting the load. Such devices commonly employ a movable member driven by the power piston and a stationary element. For example, the energy absorbing device may be in the form of a compressor having a piston movable in a cylinder. My apparatus contemplates that where the movable member moves too far as, for instance, if the compressor piston moves too close to the compressor cylinder head, means responsive to such excessive movement causes the return energy to be adjusted independently of the knock responsive means so as to reduce the compression ratio and hence to educe the extent to which the movable driven member is moved by the power piston. The sensing means in such case may take the form of an element di rectly engaged by the movable member when it moves too far. Thus, in the case of a compressor, the element may be a member directly engaged by the piston when it moves too close to the cylinder head. Again, a portion of the air in the compressor chamber may be employed for the controlling action.

Various other objects and features of the present invention will be apparent from a consideration of the accompanying specification, claims and drawings.

BRIEF DESCRIPTIONS OF THE DRAWINGS FIG. 1 is a schematic view showing a free piston engine in longitudinal cross section and incorporating the improved knock control features of the present invention;

FIG. 2 is a schematic view of modified form of my invention employing a pneumatic control for varying the return energy and also showing means for guarding against excess movement of the movable member driven by the power piston;

.FIG. 3 is a fragmentary view showing a modified arrangement for sensing excessive movement of the driven member; 1

FIG. 4 is a schematic view of a further modification in which there are alternately acting power pistons, each power piston and cylinder acting to provide the return energy for the other piston and in which there are sensors responsive to incipient engine knock, which fuel pumps are individually adjusted depending upon the incipient knock condition in the cylinder opposite to that with which the fuel pump is associated. Throughout the various figures of the drawings, the same reference numerals have been used to designate the same or identical parts or elements in the various embodiments of the engines shown. Furthermore, when the terms right, left, right end, and left end are used herein, it should be understood that these terms have reference only to the structure shown in the drawings, as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT EMBODIMENT OF FIG. 1

In FIG. 1, I have shown my invention as applied to a free piston engine of the type shown in my prior US. Pat. NO. 3,501,088. Such a free piston engine includes a power section 12, a balancer-synchronizer section 13 and an energy absorbing device shown schematically at 14. The energy absorbing device 14 may be a compressor such as shown in the drawing, a pump, a generator, or other device which utilizes or absorbs reciprocatory power.

Describing first the power section 12, this comprises a cylinder housing 15 which has a power cylinder 16 formed therein. A power piston 17 having an outer face 18 is positioned within the cylinder 16 for reciprocal movement therein. The piston 17 is provided with a skirted side wall 21. Piston rings 22 are carried in grooves formed in the piston 17 for minimizing the leakage of gases between the cylinder 16 and the piston 17. The left-hand end of the cylinder housing 15 is closedto form a cylinder head 24, which with the outer face 18 of the piston 17 define a combustion chamber 26 in the cylinder 16.

, Secured in and extending through the head 24.is a spark plug 25 which is connected to any suitable ignition wire 28 leading to a suitable source of ignition voltage. Also secured and extending through the head 24 is a conventional fuel injector unit 27 which is connected to a suitable fuel supply pipe 29. As will be described later, the piston 17 is moved towards the head 24 by a return energy means. By proper selection of the amount of return energy, air is compressed to a desired extent in combustion chamber 26 by the leftward movement of piston 17. During the compression stroke, fuel is introduced into the cylinder through the injector 27 and at an appropriate time in the compression cycle, the spark plug 25 is fired to cause the mixture of the fuel introduced by injector 27 and the air to be ignited. The compression ratio is the ratio between the volume of the combustion chamber at the time when the compression of the air in thechamber begins and that at the time in the engine cycle that piston 17 movesclosest to the head 24. This compression ratio depends upon the return energy available to move the piston and, as will be described, the present invention contemplates means for varying this return energy in order to control the compression ratio so as to prevent knocking.

The cylinder housing 15 is provided with inlet and exhaust ports. Typical inlet openings are indicated by the numeral 31 and a typical one of these exhaust openings is indicated by reference numeral 32. It will be understood that there may be a plurality of intake openings 31 and exhaust openings 32. The exhaust openings 32 are somewhat closer to the cylinder head than the inlet openings 31 to insure scavenging of the exhaust gases.

Referring now to the balance and synchronizing mechanism, the details of this mechanism form no part of the present invention, being described in detail in US. Pat. No. 3,525,102, granted Aug. 18, 1970, to the present inventor. Briefly, the synchronizer balancer is located in the housing 35 and comprises a double rack member 36 which is connected to and coaxial with the piston rod 37 secured to the piston 17. The synchronizing mechanism 13 also includes a pair of pinions 38 and 39 which are mounted for rotation about fixed axes. The pinions 38 and 39 engage two spaced rack members 40 and 41 which are held together by side plates, only 42 of which appears in the drawing. As the piston rod 37 moves to the right as a result of the firing of the combustible mixture within the combustion chamber 26, the rack member 36 operating through the pinions 38 and 39 is effective to move the assemblage comprising the rack members 40 and 41 and the side plates to the left and hence balance the forces imparted to the engine by the movement of all of the parts movable with rod 37. The function of the synchronizer assembly is, as pointed out above, more fully described in the above-mentioned Braun US. Pat. No. 3,525,102.

As pointed out above, the energy absorbing device 14 is shown as a compressor. This consists of a cylinder housing forming a compressor cylinder 51 in which moves a compressor piston 52 secured to a piston rod 53 which in turn is secured to the double rack member 36 and the power piston rod 37, compressor piston rod 53 being coaxial with power piston rod 37. In other words, power piston 17, double rack 36, piston rod 53, and compressor piston 52 move as a unit. The piston 52, like power piston 17, may be provided with piston rings 55 carried in grooves formed in the piston 52.

Secured to the end of the cylinder housing 50 is a cylinder head 56. The cylinder head 56 is provided with an inlet passage 58 therethrough which is closed during the compression stroke of piston 52 by a check valve 59 which opens inwardly to admit air on the suction stroke of piston 52. The cylinder head 56 is also provided with an outlet passage 61 which is closed during the suction stroke of piston 52 by an outwardly opening check valve 62. Passage 61 may lead to a suitable reservoir for maintaining the compressed air under pressure. Valves 59 and 62 are normally biased so as to aid the seating of these valves.

In normal operation, piston 52 and power piston 17 are abruptly moved to the left by reason of the pressure existing on the right-hand side of piston 52. As piston 52 moves to the left, outlet valve 62 will close as soon as the pressure on the outlet side of valve 62 is greater than the pressure between the piston 52 and the head 56. Inlet valve 59 will open as soon as the pressure between the piston 52 and the head 56 falls below the pressure existing upstream of valve 59 and air is drawn into the compression chamber between piston 52 and head 56. The two pistons 17 and 52 continue to move to the left. During the time the inletopenings 31 were opened by movement of the piston 17 to the right, air was admitted into the combustion chamber through the inlet openings 31. As previously explained, fuel is injected through injector 27 and the compressed fuel mixture is ignited by the spark plug 25. Upon firing taking place within the combustion chamber, the piston 17 is moved rapidly to the right, also moving the compressor piston 52 to the right to compress the air which has drawn in through the inlet opening 58. As the air is compressed, it passes out through the outlet opening 61 to a suitable air reservoir under pressure.

The air compressed by compressor piston 52 thus is I not only supplied to a reservoir but also acts as the medium in which the return energy necessary to move the piston 17 in its compression stroke is stored. In other words, the compressor piston 52 and the compressor cylinder 51 act as part of the return energy means for power piston 18. The action of this return energy means is partially opposed by a bounce chamber 65 on the left-hand side of piston 52. This chamber exists between the left-hand side of piston 52 and a partition wall 66 between the left-hand end of cylinder 51 and the housing 35 for the synchronizer 13. The bounce chamber may be either a positive or negative bounce chamber depending upon whether the effect of the chamber is to add to or subtract from the return energy available to move the power piston on its compression stroke. As illustrated, the chamber functions as a mega tive bounce chamber in that a pressure is built up as piston 52 moves to the left, this pressure retarding the movement of compressor piston 52 and power piston 17 during the compression stroke of the latter. An opening 67 extends through the wall of the cylinder housing 50 and inserted into this opening is an inwardly opening check valve 68, biased to closed position, which communicates at its outer end with a restricted orifice member 69. An opening 71 also extends through the wall of cylinder housing 50 and secured in this opening is a pressure biased outlet valve 72. This outlet valve 72 has a passage 73 communicating at its lower end with the interior of the bounce chamber 65. At its upper end, the passage 73 terminates in a valve seat upon which a valve member 75 is adapted to seat. The valve member 75 controls the communication between passage 73 and an exhaust opening 74. A chamber 76 is formed between the upper space of valve member 75 and the outer wall of the housing of the valve 72. The pressure in this chamber determines the bias on valve member 75. Air is supplied to chamber 76 through the conduit 78 leading from a source of control fluid 79. The flow of control fluid from source 79 to the chamber 76 is controlled by a valve 80. Air or any other control fluid being used is allowed to continuously escape from chamber 76 through a bleedorifice 81. Thus, the pressure in chamber 76 is dependent upon the size of the orifice 81 and the extent to which valve 80 is opened. While the valve 80 is open, the pressure tends to build up in chamber 76 forcing valve member 75 harder against its seat. Whenevervalve 80 is closed, the pressure bleeds off through orifice 81. Fluid escaping through orifice 81 may be suitably recirculated, if desirable.

The valve 80 is operated by an electrical solenoid 82 or any other suitable actuator. The energization of solenoid 82 is controlled by a sensor 84 secured to the head 24 of the power cylinder 15. Sensor 84 may be any suitable device for responding to vibrations of an engine element indicating incipient knocking and which is effective when subjected to such vibrations to produce an electrical signal. Devices of this type are well known and need not be described in detail. A typical device of this type is that shown in the Lancor US. Pat. No. 2,619,605. The output of sensor 84 is connected through an electrical conductor 85 and a ground connection 86 to a suitable electronic amplifier 87 supplied with power by input power leads 88 and 89. The amplifier preferably has some conventional means for filtering or otherwise modifying the signal to provide a relatively uniform output. The output of amplifier 87 is applied through conductors 90 and 91 to the solenoid operator 82 of valve 80. Thus, whenever sensor 84 detects incipient knocking of the engine 12, it produces a signal which is amplified and filtered in amplifier 87 and causes energization of the solenoid 82 to open valve 80 admitting pressure fluid from the source 79 through line-78 to the chamber 76.

Referring now to the operation of the bounce chamber 65, whenever the compressor piston 52 moves to the right in a compressing direction, air tends to be drawn into the bounce chamber 65 through the restricted orifice 69 and the check valve 68. By reason of the restricted orifice 69, the amount of air so drawn in is somewhat limited. When compressor piston 52 moves to the left during the compression stroke of the power piston 17 as a result of the energy stored in the air which has been compressed between compressor piston 52 and cylinder head 56, the check valve 68 closes and the pressure in bounce chamber 65 tends to build up. If it builds up beyond a predetermined value corresponding to the pressure in the pressure chamber 76 of valve 72, the valve member 75 is moved away from its seat to permit escape of air through the passage 3 and-the exhaust passage 74. The pressure finally existing in bounce chamber 65 as the compressor piston 52 approaches the end of its stroke to the left, thus depends upon the pressure in chamber 76 which in turn depends upon the operation of sensor 84.

Referring now to the overall operation of the unit of FIG. 1, when the fuel mixture within the combustion chamber 26 is fired after the compression stroke of the power piston 17, the piston is driven to the right to cause compressor piston 52 to likewise move to the right and compress the air which has been drawn in through inlet opening 58. This not only results in compressed air being delivered to a suitable reservoir through the outlet passage 61 but also results in energy being stored on the right-hand side of the piston 52 for causing its return to the left. At the same time that piston 52 moves to the right, air in the bounce chamber 65 expands and a very small amount of air is drawn into the chamber 65 through the check valve 68. The return energy stored in the air which has been compressed to the right of piston 52 is now effective to move compressor piston 52 to the left and hence to move power piston 17 to the left so as to cause compression of the air which has entered chamber 26 through air inlet openings 31. The extent to which piston 17 moves to the left is dependent upon the amount of return energy available. This is determined not only by the amount of air and its pressure on the right-hand side of piston 52 when the piston 52 is at its nonnal reversal point near' cylinder head 56, but also by the pressure in negative bounce chamber 65. The pressure of the air on the right-hand side of piston 52 is normally relatively constant due to the demand for a constant pressure-in the air reservoir to which outlet passage 61 is connected. in other words, the pressure available for moving 7 power piston 17 in its compression stroke is dependent upon the total return energy available, this return energy being the result of the opposing energy factors on opposite sides of compressor piston 52. Since, the energy on the right-hand side of piston 52 is normally relatively constant and cannot be adjusted independently of load and compressor discharge pressure, adjustment is made of the pressure in the bounce chamber 65. This is done by adjusting the pressure in the pressure chamber 76 acting on the valve member 75.

Whenever the vibration sensor 84 senses the vibration associated with an incipient knock of the engine, the sensor is effective to produce an output which results in the energization of solenoid operator 82 to open valve 80 admitting pressure from the source 79 of control fluid to the pressure chamber 76. This will result in an increase in the pressure in this chamber to bias valve member 75 more firmly into engagement with its seat requiring a greater pressure in chamber 65 before valve member 75 can be released. This in turn prevents compressor piston 52 and power piston 17 from moving as far to the left as was previously the case. Thus, the compression ratio is reduced to in turn reduce the tendency of the engine to knock. The solenoid operated valve 80 will reopen each cycle until the sensor has detected that any tendency to knock has disappeared. Thereafter, the solenoid valve 80 remains closed and the pressure accumulated in chamber 76 starts to reduce due to the control fluid bleeding off through the bleed orifice 81. This will reduce the pressure in chamber 76 reducing the bias on valve member 75 and hence reducing the ultimate pressure in bounce chamber 76. This will in turn permit pistons 52 and 17 to move further to the left, again increasing the compression ratio. This effect will continue until the sensor 84 again detects an incipient knock condition at which time the process will be repeated. It will thus be apparent that the pressure in negative bounce chamber 65 is continuously adjusted up and down in such a manner that the compression ratio within the power cylinder 12 is always close to but slightly less than the value at which sustained knocking occurs. Since, as previously pointed out above, it is desirable to operate an engine as close to a knock condition as possible, this will result in maximum efficiency of the engine under any given set of operating conditions.

MODIFICATION OF FIG. 2

In FIG. 2, I have shown a modified form of my invention in which a mechanical instead of an electrical means is employed for sensing an incipient knock condition and controlling the bias on the outlet valve of the bounce chamber and in which the bias on this valve is also controlled by means responsive to the position of a movable member driven by the power piston.

Except for the means for sensing an incipient knock condition, the power section 12 is the same as in FIG. 1. The same reference numerals have been applied and it is believed unnecessary to repeat the description of this section of the apparatus except for the knock sensing element which will be described later. Similarly, the

balancer synchronizing section 13 is the same and similar reference characters have been applied to this.

As with the species of FIG. 1, the energy absorbing device 14 is in the form of an air compressor having a compressor piston 52 movable in a compressor cylinder housing 50 defining a compressor cylinder 51. There are also inlet and outlet check valves 59 and .62

which function in the same manner as the inlet valves 59 and 62 of FIG. 1.

One difference between the engine of FIG. 2 and that of FIG. 1 is that in addition to the negative bounce chamber 65, there is also a positive bounce chamber 102. This is formed by elongating the housing so that it is somewhat longer than the one in the engine of FIG. 1. An inner cylindrical housing 103 extends to the right from the partition wall 66 and this housing defines a cylinder 105 in which moves a bounce piston 106. The space within cylinder 105 to the left of piston 106 may be in free communication with the space within the balancer synchronizer section or may communicate with any other area at atmospheric pressure so that no substantial pressure exists to the left of piston 106. The cylindrical housing 103 is provided with suitable means (not shown) for admitting air on the right-hand side of piston 106 when the piston is moving to the left but not permitting its escape when the piston is movign to the right. The result is that when the piston 106, which is driven by the power piston 17, is moved to the right after the firing of the combustible mixture takes place, a very high pressure can be built up on the right-hand side of piston 106. This pressure acts to aid the pressure on the right-hand side of compressor piston 52 in causing movement of the power piston 17 in its compres sion stroke. In other words, the energy stored to the right-hand side of the bounce piston 106 becomes part of the total return energy available to move the power piston in its compression stroke.

If desired, the pressure in the positive bounce chamber existing on the right-hand side of bounce piston 106 could be controlled to prevent knock. In'such a case, the pressure in this chamber would be reduced whenever an incipient knock condition exists. I have, however, again shown the control of the return energy as being effective through a control of the pressure in the negative bounce chamber 65 justas in FIG. 1. As in FIG. 1, there is an inlet check valve 68 through which air can be drawn when the compressor piston 52 is moving in its compression stroke, that is to the right. The air is drawn through a restricted orifice 69. Similarly, there is a biased outlet valve 110 for permitting escape of some of this air. This biased outlet valve 110 corresponds generally in function to valve 72 of FIG. 1. It is secured in an opening 1 11 in the extension of the cylinder housing 50 and has a passage 112 communicating with the interior of the bounce chamber 65. This passage 112 is adapted to communicate with a bleed opening 117 under the control of a valve member 113. The valve member 113 is provided with a stem 1114 secured to a diaphragm 115 forming part of a pressure motor 116. The pressure motor is formed of two housing members 124 and 1 18 between the flanges of which the diaphragm 115 is clamped. The chamber between the diaphragm 115 and upper housing memberl24 is open to the atmosphere, there being a passage 119 therethrough. The chamber between the lower housing member 118 and diaphragm 115 constitutes the pressure chamber of the pressure motor 116. Fluid is admitted to this chamber through a conduit 120 extending into the chamber. A restricted bleed 121 is also connected to the chamber below diaphragm 115. A suitable biasing means, such as spring 125, is interposed between the inner wall of housing member 118 and diaphragm 115 and acts to bias valve member 113 against its seat. The biasing effect of spring 125 is augmented by the fluid pressure in the chamber beneath diaphragm 115 so that the total bias exerted on valve member 113 is the sum of that exerted by spring 125 and the fluid pressure exerted on diaphragm 115. In a manner similar to the way in which pressure is maintained in the pressure chamber 76 of valve 72 of the species of FIG. 1, the pressure in the chamber beneath diaphragm 115 is varied by selectively admitting air through conduit 120 to this pressure chamber at a rate greater than it can bleed off through the restricted bleed 121. The conduit 120 is connected through a conduit 122 to the outlet opening of a pilot valve 126, the inlet of which is connected to a source 127 of compressed air. This source of compressed air, like source 79 of FIG. 1, may be the reservoir of compressed air which is supplied by the compressor 14. The pilot valve 126 includes a valve member 128 biased into engagement with a valve seat 129 by a spring 130. The valve member 128 is normally maintained in engagement with the valve seat 129 by the spring 130; in other words, the pilot valve 126 is normally closed.

Connected to valve member 128 is a valve stem 131, the outer end of which engages a rocker arm 133 pivotally secured to cylinder head 24 by a pivot pin 134. The opposite end of rocker arm 133 has an adjusting screw 135 extending therethrough. The inner end of this adjusting screw 135 engages an anvil 136 secured to the head 24. The adjusting screw 135 is normally adjusted so that valve member 128 is held in closed position by biasing spring 130 when the engine is operating in a normal manner. When, however, an incipient knock condition occurs, the anvil 136 is vibrated causing arm 133 to be rocked in a counterclockwise direction to open the pilot valve 126 and admit air from the source 27 of compressed air through conduits 122 and 120 to the underside of the diaphragm 115. Thisresults in the pressure in the chamber beneath diaphragm 115 increasing to bias valve member 113 more firmly against its valve seat.

The operation of the apparatus of FIG. 2, as described so far, is very similar to that of the apparatus of FIG. 1. Whenever the anvil 136 detects incipient knocking, pilot valve 126 is opened to increase the pressure beneath diaphragm 115 and hence to increase the bias on valve member 113. Just as with pilot valve 72, this results in increasing the pressure in the negative bounce chamber 65 to decrease the movement of the power piston 17 towards the cylinder head during its compression stroke. This, in turn, reduces the compression' ratio to reduce the tendency of the engine to knock. This, in turn, results inreclosure of pilot valve 126 to interrupt the flow of fluid through conduit 120 to the underside of diaphragm 115 to reduce the bias on valve 113. This will in turn result in the piston 17 moving closer to the cylinder head 24 and again increasing the compression ratio. This will continue until incipient knocking is again detected at which time the process will be repeated. Thus, as with FIG. 1, the compression ratio is constantly adjusted to maintain the engine operating at a point close to that at which it could knock.

In FIG. 2, I have provided an additional means of varying the return energy to vary the compression ratio. In a free piston engine in which there is no crankshaft, it is possible under some conditions for the movable member of the energy absorbing device to be moved too far by the power piston when combustion occurs. In a crankshaft type of engine, the movement of the driven member is definitely limited by the crankshaft. This is not true, however, in a free piston engine. The present invention contemplates the provision of means to change the compression ratio of the engine if the movement of the movable member of the energy absorbing device becomes too great. Where the energy absorbing device is, for example, a compressor having a compressor piston movable within a cylinder, the present apparatus senses when the compressor piston approaches too close to the cylinder head of the compressor cylinder.

Referring specifically to the apparatus shown in the drawing, a pilot valve 140 is provided for controlling the flow of fluid from a pipe 141 connected to a source of air under pressure through a pipe 123 to conduit leading to the chamber beneath diaphragm 115. The pilot valve comprises a valve member 142 normally biased into engagement with a valve seat 144 to interrupt the flow of fluid from the air source through pipe 141. The valve member 142 is normally biased into engagement with seat 144 by a spring 143. Secured to valve member 142 and extending through the housing of pilot valve 140 is a valve stem 145, the inner end of which lies in the path of compressor piston 52 and which will be engaged by the head of compressor piston 52 if the piston 52 approaches too closely to cylinder head 56. When this happens, the piston head is effective to force valve steam 145 and valve member 142 to the right, moving valve member 142 away from its seat 144 and permitting air to flow from the source of air through pipe 141 and conduits 123 and 120 to the interior of the pressure chamber beneath diaphragm 115. This results in increasing the bias on outlet valve 113 to increase the pressure in the bounce chamber 65 and hence decrease the compression ratio in the manner previously described in connection with the action of the detonation sensor. Thus, even though the detonation sensor including rocker arm 133 and anvil 136 may not be sensing any incipient knock condition, the apparatus including pilot valve 140 will still reduce the compression ratio if the piston 52 approaches too closely to the piston head 56. It will be obvious that if the compression ratio is reduced, the force exerted on the piston 17 during the firing operation will be decreased and the piston 17 will not move compressor piston 52 as far as it would otherwise. Thus, the apparatus of FIG. 2 is effective to cause the return energy operating the piston to be changed either in the event of an incipient knock condition or in the event of the movable member of the energy storage device moving too far. Furthermore, the arrangement of FIG. 2 exerts its controlling action without the use of electrical energy so that electrical connections to an external source of electrical power are unnecessary.

MODIFICATION OF FIG. 3

In FIG. 3, l have shown a slight modification of the apparatus of FIG. 2. In FIG. 2, the conduit 141 led to some external source of compressed air. In the arrangement of FIG. 3, this connection to an external source of compressed air is omitted and the compressed air on the right-hand side of piston 52 is used for the controlling effect. The pilot valve of this unit is similar to pilot valve 140 of FIG. 2 with the exception that instead of being connected to a conduit 141 leading to a source of compressed air, the valve seat 144 communicates with the interior of the chamber between piston 52 and cylinder head 56 through a passage 151. Thus, when the stem 145 of valve member 142 is engaged by the head of the compressor piston 52 to move valve. member 142 away from its seat 144, fluid is admitted directly from the chamber on-the right-hand side of compressor piston 52 through conduit 123 to the space beneath the diaphragm 115.

While the arrangement of FIG. 3 is simpler in avoiding connection to an external source of pressure fluid, it is only feasible where the fluid being compressed is some harmless fluid, such as air which can be readily used as the controlling fluid. Where the fluid being compressed is a dangerous gas, it is desirable to use the arrangement of FIG. 2 in which it is possible to use a relatively harmless fluid from a different source as the control fluid.

SPECIFS OF FIG. 4

In FIG. 4, I have shown a modification in which there are two alternately acting power pistons. In this case, the combustion chamber of each power piston acts to provide the return energy for the other power piston. In this modification, the return energy available is changed by modifying the amount of fuel admitted to the combustion chamber of the cylinder opposite to that in which knocking is occurring. Actually, in FIG. 4, when knocking is about to occur in either cylinder, the amount of fuel delivered to both cylinders is decreased.

Since the left-hand power section is identical to power section 12 of FIG. 1 as far as the present invention is concerned, the same numerals have been employed in connection with the left-hand power section as were employed in connection with power section 12 of FIG. I. It is not believed necessary to again describe this power section since its structure and operation correspond with that of FIG. 1. Similarly, the right-hand power section is a mirror image of the left-hand power section. In order to enable a ready comparison of the reference numerals of the two power sections, equivalent elements in theright-hand power section have been assigned numbers 200 higher than are assigned to the same elements of the left-hand power section. Thus, the right-hand power section is designated by the reference numeral 212 and the power piston by the numeral 217. Again, it is believed unnecessary to describe power section 212 since its operation will be obvious through the previously described operation of power section 12 of FIG. 1.

The balancer synchronizer section 13 is likewise the same as that of FIG. 1 and the same reference characters have been employed in connection with this balancer synchronizer section as were employed in connection with this section in FIG. I.

The energy absorbing device 14 is driven by both power sections 12 and 212. Again, this takes the form of a compressor with a compressor piston 252 moving within a cylinder 251 formed by the cylinder housing 250. Due to the fact that the compressor is a doubleacting compressor, its construction is somewhat different from that of the compressor of FIG. 1. Accordingly, for those elements which do not correspond with elements of the compressor of FIG. 1, numerals in the 100 series are assigned to these elements. Secured to the opposite ends of cylinder housing 250 are end walls 155 and 156. These end walls are secured in gastight relation to the ends of the cylinder housing 250 by means (not shown) and constitute the ends of thecylinder 250. End wall member is provided with a curved inlet passage 161 leading to the interior of the cylinder 251 on the left-hand side of piston 252. It will be understood that there will be an outwardly closing check valve in series with passage 161 so as to prevent escape of the gas compressed by piston 252. Similarly, end member 155 has an outlet opening 162 communicating at its inner end with the interior of the cylinder 251 on the left-hand side of piston 252. The passage 162 may lead to a suitable air reservoir for storing air under pressure. lnterposed in the connection extending from passage 162 will be an inwardly closing check valve to prevent return of air to the cylinder from the air reservoir. Similarly, end wall 156 is provided with passages 163 and 164 which correspond in function to passages 161 and 162, respectively. Again, passage 163 will lead to a source of gas to be compressed and will be provided with an outwardly closing check valve whereas passage 164 will lead to a container for the compressed gas and will be provided with an inwardly closing check valve. It will be obvious that when piston 252 moves to the right, air or other gas to be compressed is drawn in through passage 161. At the same time, compressed gas on the right-hand side of the piston is forced out through outlet passage 164. When the piston 252 moves to the left, the gas being pumped will be drawn in on the right-hand side through opening 163 and compressed gas will be forced out through passage 162.

A pair of mechanically operated fuel injection pumps 166 and 167 are secured to the housing 35 of the synchronizer balancer section 13. The rank sectionv 240 corresponding to rack section 40 of FIG. 1 is provided with a cam slot 168. This cam slot has a flat intermediate portion-and sloping end portions. Cooperating with this cam slot are plungers 169 and 170 which act, when reciprocated, as the pumping elements of pumps 166 and 167, respectively. Whenever these are reciprocated, fuel is pumped from inlet pipes 172 and 173 to outlet pipes 174 and 175. Theoutlet pipes or conduits lead to injectors 27 and 227,.respectively- The. inlet pipes or conduits 172 and 173 are connected to a suitable fuel source through a conduit 175 and branch conduits 176 and 177. The amount of fuel pumped by pumps 166 and 167 as plungers 169 and 170 are reciprocated depends upon the position of the fuel rack 180. Such fuel racks are quite customary in connectionwith fuel injector pumps. They may, for example, be employed to vary the proportion of the effective stroke of the piston during which the intake valve is open. Since such fuel racks are quite common in connection with fuel pumps, it is believed-unnecessary to describe this operation beyond stating that when rack 180 is moved to the right, as viewed in FIG. 4, the amount of fuel delivered by pumps 166 and 167 is decreased. Conversely, when the rack is moved to the left, the amount of fuel delivered is increased.

Referring now to the overall operation of fuel pumps 166 and 167, it will be apparent that when the rack member 240 of the synchronizer balancer section 13 is moved to the left to the position shown as a result of power piston 17 being forced to the right during the firing stroke, plunger 170 of fuel pump 167 is raised. When the fuel mixture in chamber 226 of the righthand power unit 212 is fired so that power piston 217 moves to the left, the rack 240 will move to the right causing the plunger 170 to ride downwardly in the groove 168 and plunger 169 to be raised upwardly as it is engaged by the inclined portion on the left-hand side of groove 168. Thus, as the pistons 17 and 217 are alternately moved in their firing strokes, plungers 169 and 170 are alternately operated to cause alternate operation of pumps 166 and 167. Pump 166 is operated to supply fuel to injector 27 during the compression stroke of power piston 17; pump 167 is operated to supply fuel to injector 227 when power piston 217 is moving in its compression stroke. The amount of fuel being delivered in each case depends upon the position of rack 180. This in turn depends upon the pressure within the pressure chamber of a fluid motor 182. The fluid motor 182 generally corresponds with motor 116 of FIG. 2, there being a diaphragm 183 forming one wall of a pressure chamber 184 having an inlet 185 for air under pressure and a restricted constant bleed 186. The diaphragm 184 may be spring biased, as shown at 187. The pressure in chamber 184 will oppose this biasing means. The diaphragm 183 is connected to a rod 188 which connects to rack 180. The position that diaphragm-183, rod 188 and rack 180 take depends upon the pressure in chamber 184. This pressure depends upon the extent of time in which a valve 189 is open. This valve 189 controls the flow of fluid from a suitable source 191 to the pressure chamber 184. When the valve 189 is opened, air flows from the source 191 into the pressure chamber 184 at a rate greater than the air or other pressure fluid leaks off through the bleed 186, so that the pressure in chamber 184 rises. when valve 189 is closed, no air is admitted from source 191 and since air continues to leak off through the bleed 186, the pressure in chamber 184 falls. The valve 189, like valve 80 of FIG. 1, is controlled by an amplifier 87 corresponding to the amplifier 87 of FIG. 1. The input to this amplifier is controlled by a vibration sensitive device 84 which responds to any incipient knocking of the engine to produce an input signal to amplifier 87 which is effective to cause energization of solenoid 190 to open valve 189 and admit fluid from the source 191 to the pressure chamber 184 of the pressure motor 182 so as to tend to cause movement of rack 180 to the right. As previously explained, when rack 180 is moved to the right, the amount of fuel delivered by pumps 166 and 167 is decreased. This will in turn decrease the power by which pistons 17 and 217 are moved during their firing stroke.

The energization of solenoid operator 190 is also controlled by the vibration sensor 284 associated with the other power cylinder 212. This sen'sor functions in the same manner as sensor 84 to detect any incipient knock condition in connection with the engine 212 and when such a condition occurs to produce a signal which is supplied to the input of an amplifier 287. The output terminals of amplifier 287 are connected to the solenoid 190 sothat the solenoid 190 may be energized either from amplifier 87 or amplifier 287. Thus, in the event of an incipient knock condition in connection with either one of the power sections 12 or 212, the solenoid operator 190 is energized to open the valve 189 to permit fluid to flow from the source 191 of control fluid to the pressure chamber 184 of fluid motor 182. This will in turn cause movement of the rack to the right to decrease the amount of fuel delivered by pumps 166 and 167 to their respective fuel injectors 27 and 227. This in turn results in a decrease in the amount of fuel delivered to both cylinders and a decrease in the combustion energy available. This in turn results in a decrease in the return energy available to move the opposite cylinder since the amount of fuel being supplied to both cylinders is being decreased, neither cylinder will move as far in the compressing direction as it did previously. The reason for employing two vibration sensors is that it may occasionally happen that one cylinder and not the other will have knock condition. If either cylinder shows a tendency to knock, then it is desirable to reduce the amount of fuel supplied to both cylinders so as to stop the incipient knock condition.

While I have shown two vibration sensors, one for each cylinder, it is possible in some cases to employ a single such sensor located so as to sense an incipient knock condition in either cylinder. Such a sensor may be located, for example, adjacent to the middle of the engine. In such a case, this single sensor would control the amount of fuel supplied to both cylinders. For example, such a sensor could control through an amplifier the operation of solenoid 190.

OPERATION OF SPECIES OF FIG. 5

In FIG. 5, I have shown a modification in which instead of using a mechanically operated fuel pump such as fuel pumps 166 or 167, I use an electrically operated fuel injector. The fluid motor 182 corresponds to fluid motor 182 of FIG. 4 and has the pressure within its pressure chamber 184 controlled in the same manner by a solenoid valve 189 operated by a solenoid 190 controlled by an amplifier 87, the input signal to which is controlled by a sensor 84. The stem 188 of fluid motor 182 is in this modification connected to an arm 306 controlling a potentiometer 304 forming part of a programmer for'the injector, the programmer being designated by the reference numeral 305. The output of this programmer is in turn connected to an electrically operated injector 302. Programmers of this type are quite old, being used in connection with a common type of pressure-time controlled system in which the fuel is held at a relatively constant pressure and is admitted for variable periods of time under the control of the programmer. The potentiometer 304 is shown as illustrative of any of various means by which the program of the programmer can be altered. For the purposes of the present invention, when the arm 306 is moved upwardly the potentiometer 304 is adjusted to change the program for the injector in such a manner as to decrease the amount of fuel supplied by the electrically operated injector 302 to the interior of the combustion chamber 26. Whenever the pressure within pressure chamber 184 of fluid motor 182 increases, the arm 306 is moved upwardly to decrease the fuel in the manner just described. Thus, the operation of the modification of FIG. 5 is the same as that of FIG. 4 with the sole exception that instead of the injectors being mechanical injectors supplied by mechanically driven pumps, the injectors are electrical injectors which inject the' fluid, the amount of fluid being injected being controlled by a programmer. While I have shown only one injector 302, it is-to be understood that the programmer 305 can control a similar injector for the other power cylinder so that, as in FIG. 4, if the sensor associated with either cylinder senses an incipient knock condition, the amount offuel injected into both cylinders is decreased.

MODIFICATION OF FIG. 6 v

The modification of FIG. 6 differs from that of FIG. 4 in that the fuel pumps are individually controlled in accordance with a knock condition existing in the opposite cylinder. In other words, if an incipient knock in one cylinder is detected, the mechanism is effective to alter the output only of the fuel pump delivering fuel to the opposite cylinder.

Referring specifically to the drawing, two fuel injection pumps are indicated by the reference numerals 315 and 316. These pumps may be driven by any suitable means such as by a connection to a moving part of the engine, as in FIG. 4. Fuel pump 315 has associated therewith a rack 319 for adjusting the fuel output of pump 315 in a manner similar to that in which rack 180 adjusted the fuel output of the two fuel pumps 166 and 167. The position of rack 319 is controlled by a pressure motor 320 which has the pressure in its pressure chamber varied in accordance with the operation of a solenoid valve 321 which is in turn controlled by one of the vibration sensors. Referring to FIG. 4 for the moment, the fuel pump 315 of FIG. 6 controls the fuel to the power section 212 and the solenoid valve 321 is controlled by the vibration sensor 84 associated with the power section 12. Thus, if an incipient knock condition is detected in connection with power section 12, the solenoid valve 321 will be opened to supply fluid to the pressure chamber of pressure motor 320 to cause rack 319 to be moved to the right to decrease the delivery of fuel by pump 315 to the combustion chamber of power section 212. This will decrease the extent to which power piston 17 of power section 12 is moved in its compression stroke and thus decrease the likelihood of any knock occurring in cylinder 26. Again, as with all of the other modifications, the absence of any incipient knock condition will result in closure of valve 321 and the pressure in the pressure chamber of pressure motor 320 will gradually decrease so as to increase again the delivery of fuel by fuel pump 315 to power section 212. The return energy supplied by power section 212 to power section 12 will thus be constantly adjusted back and forth between a value in which a knock condition is about to occur in power section 12 and one in which no knock condition occurs. Thus, the power section 12 is always operated very close to the point at which a knock condition wouldoccur.

Referring now to the other injection pump 316, this is connected with an outlet pipe 318 leading to the combustion chamber of power section 12. The output of fuel pump 316 is adjusted by a rack 324 which is connected to a pressure motor 325, the, pressure in the decrease the output of pump 316 and hence to de- 6 to the right and hence decrease the compression stroke of the power piston 217 of power section 212.

SUMMARY gine to knock. This is accomplished by the use of a condition responsive means responsive to a condition associated with possible knocking of the engine and providing controlling means controlled by this condition responsive means for controlling the return energy means. The return energy means may either take the form of a bounce chamber or may be a further power cylinder that supplies energy for the compression stroke of the power piston. It will also be seen that I can control the amount of return energy electrically or this may be done mechanically. (By the term mechanically, I include the use of any suitable mechanical controls including hydraulic controls.) It will also be seen that I have provided means for limiting the movement of a movable member driven by the engine in which excess movement of such movable member also results in a change in the return energy to vary the compression ratio in such a manner as to reduce the extent to which such movable member is moved by the power piston.

While I have shown the use of two vibration sensors where alternatively acting power pistons are used, it is to be understood, as pointed out above, that a single sensor can be employed and can be located at a point where it will detect incipient knocking in either cylinder. Furthermore, while I have shown means for reducing the amount of return energy available when incipient knocking occurs, there may be cases in which it is desirable to increase the return energy to avoid continued knocking. This is particularly true in a Diesel engine where reduction in knocking may be accomplished by increasing the compression ratio.

In general, while I have shown certain specific embodiments of my invention, it is to be understood that this is only for purposes of illustration and that the scope of my invention is limited solely by the appended claims.

I claim as my invention: 1. A free piston engine comprising: a power cylinder having a power piston reciprocally movable in said cylinder and defining an internal combustion chamber with said power cylinder, and means for introducing air and fuel into said power cylinder between said piston and the head of said cylinder to form a mixture therein consisting of fuel and air, said piston being movable toward the head of said cylinder to compress the fuel mixture on a compression stroke and away from said head upon firing of the fuel mixture, return energy means operatively connected to said piston for applying return energy to said piston, said means being effective to apply sufficient return energy to said piston following the firing stroke of said engine to cause said piston to move towards the head of said power cylinder to compress the fuel mixture to the desired extent, and controlling means for so varying the amount of the return energy applied to s'aid'piston as to prevent sustained knocking of the engine, said controlling means comprising a condition responsive means having a condition sensing element located adjacent the engine and responsive to a condition normally followed by sustained knocking of the engine, and adjusting means controlled by said condition responsive means for variably controlling said return'energy means to adjust the return energy in a direction and by an amount sufficient that the resulting change in the compressionratio in said cylinder will, without interrupting the operation of said engine, prevent the occurrence of sustained knocking thereof.

2. The free piston engine of claim 1 in which the return energy means includes a bounce chamber and in which said controlling means is effective to change the pressure in said bounce chamber.

3. The free piston engine of claim 1 in which the return energy means includes a positive bounce chamber and an opposing negative bounce chamber and in which said controlling means is effective to change the pressure in one of said bounce chambers.

4. The free piston engine of claim 2 in which the bounce chamber has a check valve for admitting fluid to said chamber and a biased outlet valve for permitting escape of fluid from said chamber and in which said controlling means is effective to change the bias on said outlet valve to change the pressure in said bounce chamber. v

5. The free piston engine of claim 4 in which a fluid motor having a pressure chamber is effective to change the bias on said outlet valve and in which said condition responsive means is effective to vary the pressure in the pressure chamber of said fluid motor.

6. Thevfree piston engine of claim 1 in which said controlling means includes a fluid motor for changing the return energy available to move the power piston and in which said condition responsive means is effective to vary the pressure in the pressure chamber of said fluid motor.

7. The free piston engine of claim 1 in which there are two power pistons each movable in a power cylinder, and in which the return energy means for either piston includes the other power piston and associated power cylinder.

8. The free piston engine of claim 7 in which the controlling means is effective to control the amount of fuel admitted into the power cylinder associated with the other power piston.

livered by said pump.

10. The free piston ngine of claim 7 in which said condition responsive means is associated with said engine in such a manner as to detect possible knocking in either cylinder and in which said controlling means is controlled by said condition responsive means in such a manner that if said condition responsive means detects possible knocking in either cylinder of the engine, said controlling means is effective to reduce the amount of fuel admitted into both power cylinders.

11. The free piston engine of claim 10 in which said condition responsive means consists of a separate condition sensor associated with each cylinder and in which the controlling means is controlled by both of said condition sensors in such a manner that if either one of said condition sensors detects possible knocking of the engine, said controlling means is effective to reduce the amount of fuel admitted into both power cylinders.

12. The free piston engine of claim 10 in which there is a fuel pump associated with each cylinder with a common adjusting means for adjusting the amount of fuel delivered by both pumps and in which said controlling means operates upon said common adjusting means.

13. The free piston engine of claim 1 in which the condition responsive means is responsive to mechani- 9. The free piston engine of claim 7 in which there is a fuel pump for injecting fuel into such power cylinder associated with the other-power piston and in which said controlling means controls the amount of fuel decal vibration associated with knocking of the engine.

14. The free piston engine of claim 1 in which there is a movable member driven by said power piston and a stationary member with respect to which said movable member is moved and in which there is means responsive to said movable member moving too far with respect to said stationary member to cause said controlling means to decrease the compression ratio in said power cylinder to decrease the power output so as to decrease the extent to which said movable member is moved by said power piston with respect to said stationary member.

15. The free piston engine of claim 14 in which the movable member and the stationary element are ele ments of an air compressor and in which a portion of the air compressed thereby is employed to cause said controlling means to decrease the compression ratio in said power cylinder.

16. The free piston engine of claim 14 in which the excessive movement of said movable member is sensed by a control member lying in the path of said movable member and engaged thereby when said movable member moves too far with respect to said stationary member. 

1. A free piston engine comprising: a power cylinder having a power piston reciprocally movable in said cylinder and defining an internal combustion chamber with Said power cylinder, and means for introducing air and fuel into said power cylinder between said piston and the head of said cylinder to form a mixture therein consisting of fuel and air, said piston being movable toward the head of said cylinder to compress the fuel mixture on a compression stroke and away from said head upon firing of the fuel mixture, return energy means operatively connected to said piston for applying return energy to said piston, said means being effective to apply sufficient return energy to said piston following the firing stroke of said engine to cause said piston to move towards the head of said power cylinder to compress the fuel mixture to the desired extent, and controlling means for so varying the amount of the return energy applied to said piston as to prevent sustained knocking of the engine, said controlling means comprising a condition responsive means having a condition sensing element located adjacent the engine and responsive to a condition normally followed by sustained knocking of the engine, and adjusting means controlled by said condition responsive means for variably controlling said return energy means to adjust the return energy in a direction and by an amount sufficient that the resulting change in the compression ratio in said cylinder will, without interrupting the operation of said engine, prevent the occurrence of sustained knocking thereof.
 2. The free piston engine of claim 1 in which the return energy means includes a bounce chamber and in which said controlling means is effective to change the pressure in said bounce chamber.
 3. The free piston engine of claim 1 in which the return energy means includes a positive bounce chamber and an opposing negative bounce chamber and in which said controlling means is effective to change the pressure in one of said bounce chambers.
 4. The free piston engine of claim 2 in which the bounce chamber has a check valve for admitting fluid to said chamber and a biased outlet valve for permitting escape of fluid from said chamber and in which said controlling means is effective to change the bias on said outlet valve to change the pressure in said bounce chamber.
 5. The free piston engine of claim 4 in which a fluid motor having a pressure chamber is effective to change the bias on said outlet valve and in which said condition responsive means is effective to vary the pressure in the pressure chamber of said fluid motor.
 6. The free piston engine of claim 1 in which said controlling means includes a fluid motor for changing the return energy available to move the power piston and in which said condition responsive means is effective to vary the pressure in the pressure chamber of said fluid motor.
 7. The free piston engine of claim 1 in which there are two power pistons each movable in a power cylinder, and in which the return energy means for either piston includes the other power piston and associated power cylinder.
 8. The free piston engine of claim 7 in which the controlling means is effective to control the amount of fuel admitted into the power cylinder associated with the other power piston.
 9. The free piston engine of claim 7 in which there is a fuel pump for injecting fuel into such power cylinder associated with the other power piston and in which said controlling means controls the amount of fuel delivered by said pump.
 10. The free piston ngine of claim 7 in which said condition responsive means is associated with said engine in such a manner as to detect possible knocking in either cylinder and in which said controlling means is controlled by said condition responsive means in such a manner that if said condition responsive means detects possible knocking in either cylinder of the engine, said controlling means is effective to reduce the amount of fuel admitted into both power cylinders.
 11. The free piston engine of claim 10 in which said condition responsive means consists of a separate condition sensor associated with each cylinder and in wHich the controlling means is controlled by both of said condition sensors in such a manner that if either one of said condition sensors detects possible knocking of the engine, said controlling means is effective to reduce the amount of fuel admitted into both power cylinders.
 12. The free piston engine of claim 10 in which there is a fuel pump associated with each cylinder with a common adjusting means for adjusting the amount of fuel delivered by both pumps and in which said controlling means operates upon said common adjusting means.
 13. The free piston engine of claim 1 in which the condition responsive means is responsive to mechanical vibration associated with knocking of the engine.
 14. The free piston engine of claim 1 in which there is a movable member driven by said power piston and a stationary member with respect to which said movable member is moved and in which there is means responsive to said movable member moving too far with respect to said stationary member to cause said controlling means to decrease the compression ratio in said power cylinder to decrease the power output so as to decrease the extent to which said movable member is moved by said power piston with respect to said stationary member.
 15. The free piston engine of claim 14 in which the movable member and the stationary element are elements of an air compressor and in which a portion of the air compressed thereby is employed to cause said controlling means to decrease the compression ratio in said power cylinder.
 16. The free piston engine of claim 14 in which the excessive movement of said movable member is sensed by a control member lying in the path of said movable member and engaged thereby when said movable member moves too far with respect to said stationary member. 